1. Field of the Invention
The present invention relates to a neon discharge lamp lighting apparatus, in particular, to a neon discharging lamp lighting apparatus suitable for an indicator and the like.
2. Description of the Related Art
In the automobile industry, information machine industry, and the like, indicators are often used. A variety of light sources are used for the indicators. As an example of the light sources, a low pressure type neon discharging lamp that features a light color is known. Since the low pressure type neon discharging lamp that contains neon gas as a discharging medium has a peak of light emitting wavelength of 640 nm, which is a bright orange color, it is used for a neon sign, a brake lamp for an automobile, or the like.
In the low pressure type neon discharging lamp, discharging electrodes are air-tightly disposed at both edge portions of a glass tube. The glass tube is filled with neon gas as a discharging medium. The low pressure type neon discharging lamp is connected to an output side of a high frequency inverter. By applying a high frequency voltage from the high frequency inverter to the neon lamp, it ignites. The high frequency inverter is composed of such as a Royer circuit.
However, the conventional neon discharging lamp lighting apparatus has the following problem.
When the high frequency inverter applies a predetermined high frequency voltage to the electrodes of the low pressure type neon lamp through the discharging electrodes, bright and dark fringes or luminance irregularity takes place in the longitudinal direction of the tube of the low pressure type neon discharging lamp. Since the fringes move and stop, the lighting irregularity takes place. In other words, the low voltage type neon discharging lamp irregularly emits rays of light along the tube thereof. In an extreme case, the lamp flickeringly emits rays of light. Thus, when the neon lamp is used for a neon sign or a brake lamp for an automobile, the lamp does not occasionally provide the required indicating capability.
Japanese Patent Laid-Open Publication No. 6-196282 discloses a technology for preventing bright and dark fringes from taking place in a low pressure type neon discharging lamp. In this technology, the output impedance including a resonance condenser connected to a power supply, a ballast condenser, and so forth and the impedance of a low pressure type neon discharging lamp are designated to predetermined ranges and the lighting frequency thereof is controlled.
However, in such a lighting method using a one-transistor type driving circuit, when the capacity of the low pressure type neon discharging lamp is as large as 15 to 30 W, the capacities of the transistor and the transformer in the high frequency inverter circuit should be proportionally increased. In other words, depending on the type (standard) or capacity of the neon discharging lamp, the composition and/or structure of the high frequency inverter varies. Thus, the adaptivity as a light source for an indicator deteriorates, thereby restricting the scope of the applications thereof.